1. Field of the Invention
The present invention relates to an improvement in a speed change gear shifting system for an automotive vehicle, particularly for a motorcycle.
2. Description of the Prior Art
The invention will be described hereinafter in connection with a motorcycle in which it has found its most valuable application so far, but other applications will suggest themselves to those skilled in the art.
In a commonly used motorcycle, the clutch must frequently be disconnected whenever a speed change gear is shifted to vary the rate of power transmission. At the same time, the engine speed must be adjusted by operation of the throttle to facilitate effective and smooth shifting. Particularly, frequent and quick gear shifting and throttle work are required when highest performance is desired, such as in racing. Manually operated gear shifting mechanisms mounted on conventional motorcycles can not satisfy such requirements. On the other hand, electronically aided gear shifting systems without clutch operation are taught by Japanese Patent Application Laid-Open Publication No. 54-57724, corresponding to U.S. Pat. No. 4,270,414; and Japanese Patent Application No. 1-275489 applied for by the same inventor of this invention. In such electronically aided gear shifting systems, a sensing means senses the load applied to the shift lever or shift pedal when a driver or rider intends to shift the gear, and the ignition system is controlled in response to the data from the sensing means. However, these systems can not correctly discriminate between two types of shift load in the shift-up operation mode and the shift-down operation mode. These systems must be equipped with a complicated sensing means for differentiating between the shift-up and the shift-down shifting operation. For example, the shifting system provided by Japanese Patent Application No. 1-275489 uses a shift load sensor set on the shift pedal for sensing the shift load caused by the driver's shifting motion, and a torque sensor set on a drive chain for transmitting the engine power of a drive wheel for sensing the torque direction. These sensors cause complicated assembly work, thereby increasing cost and time in the manufacturing scene.
Further, the sensor set on the shift pedal can not correctly differentiate between whether the sensed load is caused by actual shifting work or the driver's foot only resting on the shift pedal. This causes some disadvantages, such as an unnecessary power decrease or power increase, or mis-shifting and so on.